Sodar systems employ directed sound waves to detect atmospheric phenomena such as wind speed. By directing sound beams into the atmosphere in a number of directions, and measuring the Doppler shift and intensity of echoes returned from turbulence and discontinuities in the atmosphere, wind speed and other atmospheric phenomena can be accurately estimated. The predominant type of sodar in current use is the monostatic phased array sodar. Monostatic sodar systems emanate sound beams and listen for their reflections from a single location. Phased array monostatic sodars direct the beams in different directions, and are sensitive to echoes returned from these directions, by use of an array of sound transducers which transmit and receive in groups of differing phase so as to direct the transmitted sound beams and regions of sensitivity as desired.
Historically, sodar systems have been used for research into a variety of atmospheric conditions aloft, including wind speed, turbulence, and thermal stratification and stability. Historically, considerable manual analysis and interpretation of sodar data was necessary to extract useful insight into atmospheric conditions.
Present day use of sodar systems is principally focused on the measurement of wind speed aloft, often for the purpose of assessing wind resources at candidate sites for the installation of wind turbines, but also for a variety of other purposes, for example, providing input data to weather prediction models and pollution dispersion studies. In this context the Doppler shift of the returned echo is of principal interest. Present day sodar systems rely heavily on automated detection of this Doppler shift and conversion of the Doppler shift information into radial, vertical and horizontal wind velocities. Prior art relies on relatively simple statistical methods for automatically determining a single Doppler shift in each of the several beam directions. At best, prior art methods identify periods of strong downward velocity indication as likely related to precipitation. In prior art, standard practice when collecting sodar data is to omit data during times of precipitation. This approach is not ideal since a potentially large percentage of the data acquired could be lost.
The simple statistical methods used in prior art fail to take full advantage of the spectral information available in the returned signals. The returned sound signals from the atmosphere are not simple signals with a single, clear, sharp response in the frequency domain. The response spectrum may contain multiple peaks: a peak associated with air velocity; a peak associated with fixed echoes; and a peak reflected off of rain and other precipitation. Distinguishing, separating and individually measuring these multiple peaks provides means of providing the sodar user with useful additional information as compared to prior art techniques.